Prediction of flutter characteristics for a transport wing with wingtip devices

Flutter characteristics of a transport wing with winglet and C-type wingtip were investigated using a high-fidelity aeroelastic analysis method. Unsteady aerodynamics was simulated by a computational fluid dynamics (CFD) solver where the Euler equations were presented as fluid governing equations, and structural vibration was calculated by a computational structural dynamics (CSD) solver where the modeling included geometric nonlinearity. Besides, aeroelastic analysis consisted of an effective coupling of CFD and CSD. Flutter and limit cycle oscillation (LCO) behavior of basic transport wing were predicted first, and the results were compared with the existing experiment. It was found that large-amplitude shock-wave motion provided the proper physical mechanism for the LCO. Then, flutter analyses of wingletted transport wing and C-wing were sequentially conducted. Also aerodynamic and mass effects of wingtip devices were identified separately by way of setting virtual mass. The study demonstrated that wingtip devices could produce substantial adverse effects on flutter characteristics of basic transport wing. The winglet addition, which could alter flutter mode in subsonic flow, decreased the flutter speed more than 10%. Major contributors of the winglet to variations of flutter behavior were aerodynamics and mass, respectively, for subsonic and transonic states. As for a C-wing configuration, the C-type wingtip generated a reduction of wing flutter speed up to 19%, but has a minor impact on flutter frequency. The mass of C-type wingtip dominated the effect on flutter behavior of basic transport wing.